When trolling for fish in deep water it is customary to use a control cable or line to lower a heavy weight or sinker to the approximate depth at which fishing is desired. Before lowering the weight, a short clip line is attached to the control cable near the weight or to the weight itself. A tackle line for the fisherman's rod and reel is attached to the clip line with a separable connector and the leader to the hook and bait is held with the connector. When the fishing boat is in motion the weight holds the bait at the selected depth. When a fish strikes, the connector separates so landing of the fish can be accomplished solely with the tackle line.
One disadvantage of this prior practice is that after a fish is landed or at any time that rebaiting or inspecting the bait is desired, it is necessary to raise the sinker to the level of the boat. Usually this is done by cranking the control line onto a drum or reel mounted on the boat using manual effort or an electric motor. Since fishing at depths of 50 to 150 feet or more with weights of about 15 pounds is not uncommon, it is evident that considerable energy must be expended in raising and lowering the sinker.
Using an electric motor to drive each downrigger on a single boat avoids the physical stress of manual operation, but electric motor drives create other problems. The electric motors are usually supplied from batteries aboard the boat. When there are several fisherman aboard or when the weights are raised frequently to check the condition of the bait or to remove fish, a heavy current drain is imposed on the batteries and they may become depleted and incapable of supplying the boat engine and the downrigger motors.
When doing deep water trolling, the sinker weight occasionally snags or catches on the bottom of the body of water. If detachment of the sinker cannot be accomplished by maneuvering its control cable, the cable must be cut at above water level so that the weight and a substantial part of the cable is lost.